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What Freshwater Aquarium Fish Like Soft Water?

Most freshwater fish tanks contain hard water – usually obtained from the tap and treated either by setting it out for more than 24hours or using a chemical. Did you know that most freshwater fish come from a soft water environment?  It’s true! Then we, the aquarium hobbyists, keep them in hard water.

There are many freshwater fish that like soft water such as angelfish, tiger barbs, tetras, gouramis, cory catfish, and south American cichlids. Since these fish can also adapt to hard water, they’re prime candidates for a community tank containing hard water species. However, some livebearers won’t do well in soft water, so be aware of that. 

In this article, I’ll go over some common aquarium freshwater fish that do just fine in soft water. I’ll also go over why you would want a soft water freshwater tank. Typically, saltwater tanks are soft water and not freshwater so keep reading if this topic interests you.

What Freshwater Aquarium Fish Do Well in Soft Water?

The fact is that most freshwater fish can be acclimated to a soft water environment – provided they’re introduced slowly. A drip acclimation procedure works perfectly for this situation, especially if you’re switching your tank over from hard water to soft water and have fish already establish in the aquarium.

There are some sensitive fish that won’t take to soft water very well so be aware of this before changing the water you use.

Here are my top picks for freshwater fish that do well in soft water. 

Discus Fish

The beautiful discus fish prefers soft and acidic water. They also prefer very warm water for tropical fish at 82 to 86 degrees Fahrenheit. The pH for discus fish should be in the range between 6.0 and 7.0.

Discus fish are not as forgiving as most freshwater fish therefore, it’s important to find out the water parameters of the tank you’re purchasing them from in advance so you can replicate it at home as closely as possible.

RO water is the preferred water to use in a discus tank. Using a supplement to add some needed minerals back into the water is also a good idea. Doing so will not affect the softness of the water.

Glowlight Tetras

Glowlight tetras are an extremely peaceful schooling fish that thrive in soft water conditions.

RO water is the best alternative for glowlight tetras. The pH for these colorful fish should be kept in the range of 5.8 to 7.5. When trying to breed glowlight tetras, the pH should be lowered to between 5.5 and 7.0.

The water temperature for glowlight tetras can be kept in the range of 74 to 82 degrees Fahrenheit.

glowlight tetra

Rainbow Fish

Up next is the rainbow fish. There are different types of rainbow fish such as the Boeseman’s rainbow and the Madagascar rainbow. Rainbow fish can adapt well to either hard or soft water conditions however, the Madagascar rainbow does much better.

Madagascar rainbows prefer soft acidic water with a pH in the range of 6.5 to 7.5. The water temperature for these fish should be in the range of 74 to 80 degrees Fahrenheit. 

I don’t have experience with Boeseman’s rainbow fish however, as with most like species, they can probably be drip acclimated to a softer water tank.


As with all new fish, when purchasing, you should always ask your local fish store what they have in their tanks. I say that because angelfish like slightly soft water, but I see them in hard water tanks all the time.

This means angelfish are extremely hardy and can adapt to different water conditions. If you want them to thrive however, you should have them in a slightly soft water fish tank.

RO water is a good choice for angelfish. The pH for angelfish can hover around the 7.0 mark as they like slightly soft water, not full-blown soft water.

You can also use rainwater for angelfish if your region gets a lot of rain.

South American Cichlids

Cichlids are a very popular fish in the aquarium hobby. The majority come from either south America or Africa. Regarding this article, we’re talking about South American cichlids.

South American cichlids prefer soft acidic water. I don’t know if I’ve ever heard of a local fish store telling customers this when they buy them which is a shame because we know they probably went home and put them in a hard water tank and killed the poor fish.

The pH should be in the range of 6.5 to 7.4 for south American cichlids. Water temperature should be between 75- and 80-degrees Fahrenheit. Keeping the temperature on the higher end is preferable.

German Blue Rams

The German blue ram is yet another south American cichlid however, because of its ever-growing popularity and slightly different pH range requirements, I thought it best to separate.

These are one of my favorite fish to watch. They’re full of character and color. Surely everyone can appreciate their beauty and uniqueness.

Blue rams thrive in soft water that has a pH in the range of 6.0 to 7.5. Their water temperature should be quite warm – somewhere in the range of 78 to 85 degrees Fahrenheit.

Betta Fish

Everyone reading this is likely familiar with bettas and have probably owned one at some point.

Bettas do best in a calm tank with a low current and soft, acidic water. The pH for bettas should be in the range of 6.8 to 7.5. Their tank’s water temperature should be kept quite warm – somewhere between 76- and 85- degrees Fahrenheit.


The harlequin rasbora and most other rasboras should be kept in soft acidic water.

The rasboras pH can be kept between 6.0 to 7.8 however, the lower the better. In their natural habitat with the large number of plants they dwell in, the PH can sometimes drop as low as 4.0. Keep your water temperature between 72- and 80-degrees Fahrenheit and, if possible, at the lesser end.

harlequin rasbora's

Zebra Danios

Zebra danios do best in slightly acidic mildly soft tank water.

The pH range to keep your zebra danios is 6.5 to 7.2. The fish tank’s temperature should be between 65- and 77-degrees Fahrenheit. Danios prefer their water a bit cooler than the previous fish we’ve reviewed.

The best water to use for a danios tank is a mixture of treated tap water and reverse osmosis water. This will give the slightly softer water parameters you’re trying to achieve.

The Difference between pH and Hardness Explained (for Aquarium Hobbyists)

I know for myself it took a while to wrap my head around what hardness and pH were in my fish tank, so I think it’s important to give a bit of an explanation here to help you better understand. It just makes you more capable of being able to care for your pet fish and provide them with the best life possible.

First, pH and water hardness are not the same thing. They’re both different properties in water. They’re closely linked, however.

The pH is how acidity and alkalinity are measured in water. The hardness of water is testing the existing mineral levels. If water has high mineral levels, it’ll test alkaline with a higher pH level. When there are less minerals, the water becomes soft and acidic with a lower pH level.

There are always exceptions and where you live will determine what your tap water’s pH and hardness test at. Hence, it’s always good to test your tap water, so you know how to treat the water, if necessary.

At a high level, here are some ranges for you to consider when it comes to pH and hard or soft water.

Most freshwater fish prefer a pH somewhere in the range of 6.8 to 7.6.

Hard water is more alkaline whereas soft water is more acidic (with the minerals removed). RO is a good example of acidic soft water.

RO water’s pH is between 5.0 and 7.0. Because saltwater tanks require a higher pH level (7.6 to 8.4) and RO water is the preferred source of water, you’ll have to use a chemical treatment to buffer the pH to a higher level. I’ve had luck using coral sand as substrate to buffer the pH naturally in my saltwater tanks.

The average pH for tap water in North America is 6.5 to 8.5. For information purposes, 7.0 pH is neutral.

I hope that all made sense to you…


In this article, I’ve covered some of the most popular freshwater fish that prefer a softer water environment. There are likely others that would also benefit from soft water tanks, especially when it comes to breeding.

Once you test your tap water and know what fish you want to keep, you can easily figure out if your water is soft or hard enough and if the pH needs to be adjusted.

Good luck!

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